Community > Forum > Technology & Science > Brilliant idea for re-entry

Brilliant idea for re-entry

Posted by: SuperShuki - Fri Aug 26, 2005 8:50 am
Post new topic Reply to topic
 [ 61 posts ] 
Go to page Previous  1, 2, 3, 4, 5  Next
Brilliant idea for re-entry 
Author Message
Space Station Member
Space Station Member
avatar
Joined: Tue Dec 07, 2004 6:50 am
Posts: 265
Location: UK
Post Re: kite   Posted on: Tue Aug 30, 2005 3:21 pm
campbelp2002 wrote:
nihiladrem wrote:
As the crafts orbit becomes lower the kite gets reeled in to prevent it generating too much force and either destroying itself or breaking its line.
What keeps the craft from dropping below the kite?


The kite has to be making a lot of downforce - many times its weight. It always remains in the upper-atmosphere until the craft is low enough to re-enter of its own accord. You can then do what you will with the kite. The initial deploying of it doesn't look completely straightforward though, you really want to get it stuck into the atmosphere pretty quickly otherwise the path it is likely to take will become complicated, possibly going overhead the craft without engaging the atmosphere. That would be messy. It should be possible to send out a smaller kite first and have that reel out the the full size one - the small size should make it less mass-costly to deploy quickly. Even so this would only really work for fairly low orbits, hundreds of km, not thousands.

Nick


Back to top
Profile
Moon Mission Member
Moon Mission Member
User avatar
Joined: Tue Oct 05, 2004 5:38 pm
Posts: 1361
Location: Austin, Texas
Post    Posted on: Tue Aug 30, 2005 3:29 pm
Are we talking about the same thing? The idea I am talking about is the original topic of this post, which is to slowly decelerate out of orbit over a period of many days. How long will your kite pull on the craft and how long will it take to go from orbital speed to subsonic speed?


Back to top
Profile WWW
Spaceflight Trainee
Spaceflight Trainee
avatar
Joined: Mon Aug 30, 2004 6:28 am
Posts: 43
Post    Posted on: Tue Aug 30, 2005 11:48 pm
...


Last edited by whonos on Thu Jun 07, 2007 7:18 pm, edited 1 time in total.



Back to top
Profile
Space Station Member
Space Station Member
avatar
Joined: Tue Dec 07, 2004 6:50 am
Posts: 265
Location: UK
Post    Posted on: Wed Aug 31, 2005 3:15 am
campbelp2002 wrote:
Are we talking about the same thing? The idea I am talking about is the original topic of this post, which is to slowly decelerate out of orbit over a period of many days. How long will your kite pull on the craft and how long will it take to go from orbital speed to subsonic speed?


With the kite, the drag just helps you lose altitude over maybe a day or two while keeping a nearly-circular orbit. By losing altitude you should actually be gaining some speed. The re-entry takes place in two phases, practically all the energy is still expended in the normal way during the rapid part of re-entry. This isn't a scheme which would reduce the thermal protection needed in any significant way, so perhaps it isn't on-topic.

There was recently some discussion on sci.space.science as to why spending a long time in the atmosphere during re-entry is not really possible or even necessarily good.
You can search for it using "Reentry at high temperature" in Google groups.

Nick


Back to top
Profile
Moderator
Moderator
avatar
Joined: Thu Jun 03, 2004 11:23 am
Posts: 3745
Location: Hamburg, Germany
Post    Posted on: Wed Aug 31, 2005 9:07 am
Hello, whonos,

might there be a misunderstanding? Reentry requires deceleration. Deceleration can be done quickly or slowly. Perhaps the km/s^2 can be controlled actively.

What you say regarding the angle is correct- but the speed of the increase of the angle can be controlled by controlling the amount of km/s^2. ... This seems to be the way JP Aerospace have choosen. ...



Dipl.-Volkswirt (bdvb) Augustin (Political Economist)


Back to top
Profile
Space Station Member
Space Station Member
avatar
Joined: Tue Dec 07, 2004 6:50 am
Posts: 265
Location: UK
Post    Posted on: Wed Aug 31, 2005 9:38 am
Ekkehard,
The problem is that the acceleration really can't be controlled over much range once in the upper atmosphere. In order to decelerate slowly, you need to stay at a low angle of descent. In order to do that you might try to generate lift, but in so doing you must also experience drag. The lift to drag ratio of hypersonic vehicles is very limited. That drag will make you slow down and drop in altitude, the lower speed means you need even more lift to sustain the angle of descent...Once begun in earnest the process quickly reaches a crisis point where you will de-orbit very rapidly.

JP Aerospace's plan doesn't make *any* kind of physical sense to me whatsoever.


Back to top
Profile
Moderator
Moderator
avatar
Joined: Thu Jun 03, 2004 11:23 am
Posts: 3745
Location: Hamburg, Germany
Post    Posted on: Wed Aug 31, 2005 10:50 am
As far as I have read JP Aerospace's documents and homepage their ATO has a property that is very essential and found at no other vehicle - a property that is mostly overlooked. By that property the vehicle achieves altitude.

This property is buoyancy by Helium. The ATO goes up by Helium and for this reason doesn't need high speed until a certain altitude is achieved - as far as I remember that certain altitude is somewhere around 60 km.

JP Aerospace have described that concerning "launch". At this point I have a question: Is "going up" or "gaining altitude" etc. lift? Or is "lift" something different?

According to the .pdf at their homepage the ATO gets buoyancy by very large wings of over 0,5 miles length. I suppose these wings to be filled with helium but I am not sure about that - I have asked jpowell in their official forum but said that I don't want to urge them to reveal any secrets. I didn't get an answer and so suppose that it is a secret really.

Above the " around 60 km" the ATO cannot use buoyance no longer - and so starts electric drives. The ATO seems to be able to hold 60 km altitude without them but by using them it accelerates and so gets more altitude - and achieves orbit after less than a week but more than three days.

From this all I suppose that the ATO will reenter by using the electrical drives for deceleration - and that deceleration then will require similar time as the acceleration.

When the ATO is down at 60 km altitude again it will stay there even if the drives are shut down and only will go down further if the Helium is released or cooled down again or something else.

So the Helium and the buoyancy the ATO experiences because of its design seems to get it lift which is allows it to reenter very very slowly without too much angle.

This is my personal understanding of what they say - not something I have calculated myself. jpowell himself has explained it a little bit in their official forum.

The focus of attention seems to have to be at the wings of the ATO, at the Helium and the buoyancy - the ATO is no rocket and no airplane-like vehicle like SSO: it merely is a mix of a very-high-altitude-balloon, a zeppeline and a winged vehicle. So the physics of rockets and airplanes can't be applied - the physics of balloons and zeppelines have to be applied majorly. That's my personal image I got by reading their documents and homapage as well as jpowells posts.



Dipl.-Volkswirt (bdvb) Augustin (Political Economist)


Back to top
Profile
Moon Mission Member
Moon Mission Member
User avatar
Joined: Tue Oct 05, 2004 5:38 pm
Posts: 1361
Location: Austin, Texas
Post    Posted on: Wed Aug 31, 2005 1:09 pm
whonos wrote:
as you slow down, the angle of your reentry increases exponentially
Hence my question
campbelp wrote:
What keeps the space craft up during the time that it’s speed is slower than orbital but still faster than you want to enter the lower atmosphere?


nihiladrem wrote:
This isn't a scheme which would reduce the thermal protection needed in any significant way, so perhaps it isn't on-topic.
Agreed.

nihiladrem wrote:
The lift to drag ratio of hypersonic vehicles is very limited.
I don't know much about hypersonic aerodynamics, but what you say makes sense. If there is anything NASA knows well it is hypersonic aerodynamics and they are not trying to do any extended reentry to lower heating, AFAIK. Do you have any links to hypersonic aerodynamic theory pages?


Back to top
Profile WWW
Space Station Member
Space Station Member
avatar
Joined: Tue Dec 07, 2004 6:50 am
Posts: 265
Location: UK
Post    Posted on: Wed Aug 31, 2005 1:22 pm
campbelp2002 wrote:
[ Do you have any links to hypersonic aerodynamic theory pages?

http://www.aerospaceweb.org/design/wave ... sign.shtml


Back to top
Profile
Space Station Member
Space Station Member
avatar
Joined: Thu Jan 27, 2005 12:34 am
Posts: 450
Post    Posted on: Wed Aug 31, 2005 7:26 pm
spacecowboy wrote:
Ballutes don't do any good in orbit, only during the re-entry phase. They're neat, alright, but they're still pretty massive compared to parachutes.
Since a Ballute is an inflated spherical drag system, its mass can be as little as twice an equal size parachute’s (at hypersonic velocity its drag equals that of an equal diameter parachute, but the sphere has lower drag at lower velocity, unless it is allowed to collapse into the reentrant parachute shape). Since it is inflated, deployment in near space is guaranteed, and partial inflation or deflation can be used to attenuate drag if desired. With a slightly porous nearside, small thrust from escaping gas could keep the attachment line in tension before reentry. A Ballute made of tightly woven graphite cloth would radiate the heat transferred through the reentry boundary layer, providing a reusable heat shield and allowing slightly more gradual deceleration than the optimum for ablative heat shields. A Ballute need not be much larger than the space capsule, unless it is to be used as a final parachute, and not just as a drogue in the lower atmosphere. Of course, once velocity falls from its orbital value, gravitational acceleration becomes obvious. Any large reduction in deceleration “g” load requires lift, and much more complex structures.


Back to top
Profile WWW
Moderator
Moderator
avatar
Joined: Thu Jun 03, 2004 11:23 am
Posts: 3745
Location: Hamburg, Germany
Post    Posted on: Fri Sep 02, 2005 7:40 am
What about combining the two methods - ballute and JP Aerospace's ATO-technology?

As far as I remember an article about ballutes I listed in another thread about ballutes they aare designed for vehicles and probes returning from interplanetary space and other planets while JP Aerospace's vehicles are designed for achieving and leaving orbit in the current phase of development.

So an interplanetary vehicle could be decelerated by a ballute to get into an orbit while JP Aerospace's technology could be used to reneter very very slowly.



Dipl.-Volkswirt (bdvb) Augustin (Political Economist)


Back to top
Profile
Space Station Member
Space Station Member
avatar
Joined: Tue Dec 07, 2004 6:50 am
Posts: 265
Location: UK
Post    Posted on: Fri Sep 02, 2005 8:11 am
Ekkehard Augustin wrote:
What about combining the two methods - ballute and JP Aerospace's ATO-technology?

It would help to know what JP Aerospace's ATO-technology actually was. Because without several miracles the basic plan of using ion engines and buoyancy is flawed.
To do re-entry very slowly you need to be able to be able to hold yourself up *above* the atmosphere as you slow down. There is no other way.


Back to top
Profile
Moderator
Moderator
avatar
Joined: Thu Jun 03, 2004 11:23 am
Posts: 3745
Location: Hamburg, Germany
Post    Posted on: Fri Sep 02, 2005 8:47 am
Hello, nihiladrem,

I am not sure if you read my last post about JP Aerospace - the ATO seems to be bnased on buoyancy by Helium and extremely large wings half a mile long according to their .pdf-document.

The ATO can't be compared to airplanes - especially not to supersonic airplanes. It would be worthwhile to ask jpowell in the General JP Aerospace Forum.

Additionally JP Aerospace explicitly are working on the Transatmosperical Ascender - a preliminary vehicle to the ATO.



Dipl.-Volkswirt (bdvb) Augustin (Political Economist)


Back to top
Profile
Space Station Member
Space Station Member
avatar
Joined: Tue Dec 07, 2004 6:50 am
Posts: 265
Location: UK
Post    Posted on: Fri Sep 02, 2005 9:45 am
Hi Ekkehard,
I did read your post, but I thought my reply was going to be excessive. I can't see why you maintain that it cannot be compared to supersonic airplane, it is meant to travel supersonically then hypersonically through the atmosphere, and it has to travel for several days below orbital speed at altitudes where buoyancy doesn't help. That's the information we appear to have and that information alone means it won't work.

Unless there is some technology in it to cause the thing to levitate well above the atmosphere without lift made at the expense of drag (and everything we've heard from JP suggests this is not the case) then it cannot work.

Trying to reach orbit over several days under these conditions is an extremely bad idea. If JP did have the technological miracles required to make it work I doubt I could convince them to tell me about it.

If people want to believe they have a plan which works in JP's thread, that's fine and I don't have problems with their Dark Sky Station. At the same time I really don't want people think I agree that this kind of thing is possible because from my point of view it damages the usefulness of this thread.


Back to top
Profile
Moderator
Moderator
avatar
Joined: Thu Jun 03, 2004 11:23 am
Posts: 3745
Location: Hamburg, Germany
Post    Posted on: Fri Sep 02, 2005 11:15 am
Hello, nihiladrem,

the reasons why I consider the ATO to be not comparable to a supersonic airplane are one major and several detail reasons.

The major reason is that the property to be able and to be designed to travel supersonically alone is insufficient to consider it to be a supersonic airplane - there are things travelling supersonically which no way are airplanes: rockets for example.

The detailed reasons are reasons why it can't be an airplane:

- it's designed to travel high above altitudes where airplanes can fly,
- jpowell or JP Aerospace somewhere explicitly have said that it won't work at altitudes where airplanes work because the wings are too large for that - the wings can be used at or above 42 km only,
- I have reread their document "ATO Airship To Orbit" ( www.jpaerospace.com/atohandout.pdf ) in between and found the issue "The initial test vehicle is 6,000 feet (over a mile) long." at page 2 and
- to keep the Dark Sky Station with the ATO docked to it at 42 km altitude the large ATO has to be light weight and requires something like the Helium which keeps the DSS at 42 km altitude.

From the last point I conclude the assumption that the wings will be filled with Helium perhaps - but this assumption might be wrong.

In contrary to the above detail reasons an airplane - and even a supersonic airplane -

- is designed to fly at relatively low altitudes,
- has relative small wings,
- is significantly shorter than a mile and
- would fall to the ground when docked to a Dark Sky Station because it's too heavy - even SSO fell down to below 42 km and larger wings would have made it heavier yet.

I suppose that the Helium and the very large wings play the central part in JP Aerospace's concept and cause lift a way airplanes don#t get lift. As far as I understand it airplanes get lift by speed and the shape of their wings which works in the lower atmosphere but not at and above 42 km - the air is to thin there and there is no runway to accelerate so that lift by speed is got. But the ATO explicitly will go up to 20 km without speed and without a runway - this too makes me supposing that the wings might be filled with Helium.

The whole concept of JP Airospace is based on balloons, Helium and zeppeline-like vehicles driven by propellers and electric drives - it's a third way added to airplanes and rockets.



Dipl.-Volkswirt (bdvb) Augustin (Political Economist)


Back to top
Profile
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 61 posts ] 
 

Who is online 

Users browsing this forum: No registered users and 16 guests


© 2014 The International Space Fellowship, developed by Gabitasoft Interactive. All Rights Reserved.  Privacy Policy | Terms of Use